From the general prior art aircraft with an emergency power generation device, or more generally a secondary power generation device, are of known art; the device has a mounting support and a propeller fitted to the end of the support to generate electrical energy. Such units are also designated as ram air turbines. The mounting support is installed in the fuselage or wing of the aircraft such that it can be folded out; in normal operation of the aircraft it is located in a retracted state. In an emergency situation with a decrease in the available energy the mounting support together with the propeller can be extended to generate energy.
From the general prior art aircraft with an auxiliary power generation unit (APU) are of known art; the latter is a combination of a turbine and a generator to generate power, e.g. to supply power to aircraft systems when the aircraft is standing on the ground, and optionally to generate compressed air in order to start the aircraft engines. For this purpose a turbine of the auxiliary power generation unit is mounted in a flow duct between an air inlet duct and an exhaust duct at the tip of the rear section of the aircraft.
From DE 10 2006 003 138 A1 a power supply system for integration into an aircraft system is of known art; this has a secondary power supply device in the form of an emergency supply unit. A duct runs between two openings on the fuselage of the aircraft, with a forward opening and a rearward opening, as seen in the aircraft longitudinal direction. In the duct is arranged a turbine, to which a generator is coupled. On the forward opening a covering device is provided that can be moved between a closed and an open position by means of an electromechanically actuable opening and closing device; the latter is for purposes of covering the opening in the closed position of the covering device. To this end the actuation device is functionally connected with the opening and closing device for purposes of generating an opening or closing signal.
The document U.S. Pat. No. 6,272,838 B1, the document EP 1 767 455 A2, the document U.S. Pat. No. 6,247,668 B1 and the document U.S. Pat. No. 7,222,819 B1 each describe means of control for the inlet flap of an APU.
GB 2419640 describes an APU that is provided for the purpose of temporarily generating energy in flight, e.g. in the event of an “engine out condition”. To this end the APU is arranged in a duct into which ram air can gain access to drive the APU, via an inlet that can be closed and opened by a flap.